The present invention relates to the generation of a plasma in a processing chamber, and particularly the generation of an inductively coupled high density plasma in a chamber for performing deposition and etching processes.
Inductively coupled high density plasmas are widely used in connection with processing operations that involve the deposition of layers on, or the etching away of layers from, a substrate, such as a semiconductor wafer, in the course of integrated circuit fabrication.
Apparatus of this type includes a processing chamber whose interior is maintained at a low pressure and into which a substrate, such as a semiconductor wafer, is introduced. The processing chamber is typically surrounded by coils which are supplied with a radio frequency (RF) current that results in the generation of RF magnetic fields within the processing chamber. The RF magnetic fields generate RF electric fields that accelerate electrons and the accelerated electrons act to ionize atoms and molecules. When an ionizable process material is introduced into the chamber, molecules of that material are ionized in the RF magnetic field to create a plasma. Ions within the plasma are directed at a surface of the substrate to effect either deposition of a layer on the substrate surface or etching of a layer of material from the substrate surface. Electric fields established within the processing chamber propel ions within the plasma toward and into the substrate surface. The plasma also changes the input gas in a functional system to make it more reactive. The degree of reactivity is dependent upon the density of the plasma through which the molecules travel on their way to the substrate and on the electron energy distribution of the electrons.
In virtually all processing operations of this type, it is desired to control the ion density across the surface of the substrate. Often, the action performed on the substrate should be as uniform as possible across the substrate surface, i.e. the deposited layer or the material etched from the substrate surface should have as uniform a thickness as possible. This thickness uniformity is dependent to a substantial degree on the uniformity of the electric field density and the uniformity of the plasma density in planes parallel to the substrate surface, i.e. in planes perpendicular to the longitudinal axis of the processing chamber.
A variety of coil configurations have been proposed for the purpose of controlling the RF magnetic field produced by the coils. While many of these configurations are capable of producing plasma of a reasonably uniform density, the configurations proposed to date cannot create the conditions necessary to meet anticipated future demands.